The onset of instability in a parametric resonance energy harvester under panchromatic excitations

This paper further explores the potential of parametric resonance to enhance wave energy conversion in a pendulum-based pitching floating energy harvester, considering power extraction and panchromatic excitation. Unlike traditional parametric systems that focus on inertial mechanical instability induced by floater motion, this concept, firstly proposed in a previous recent publication, leverages the parametric resonance induced by nonlinear hydrodynamic coupling between heave and pitch. By deliberately integrating parametric instability into the floater design with a 2:1 ratio of natural periods in two hydrodynamic degrees of freedom, the frequency bandwidth of the mechanical system is expanded, leading to two distinct regions of significant power production. The research advances current understanding in three key areas: (i) the use of Bezier curves to advance a computationally efficient nonlinear hydrodynamic model based on nonlinear Froude–Krylov force calculations tailored for prismatic floaters, (ii) investigation of the impact of power extraction on the severity of nonlinear parametric resonance, and (iii) consideration of more realistic panchromatic waves to quantify the onset of instability and the decrease in the severity of parametric resonance response, also addressing practical implications for numerical simulations and signal processing. Findings indicate that beneficial parametric resonance persists across various damping and wave conditions, although the relative importance of the contribution of the 2:1 parametric resonance region to power extraction decreases by 75%, on average.